拉姆达表达式 追加 条件判断 Expression<Func<T, bool>>

• 摘要：publicstaticclassPredicateBuilder{///<summary>///机关函数应用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混应时写在AND后的OR有效///</summary>///<typeparamname="T"></typeparam>///<returns></returns>publicstaticExpression<Func<T
• 标签：expression 表达式

public static class PredicateBuilder
{

/// <summary>
/// 机关函数应用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混应时写在AND后的OR有效 
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> True<T>() { return f => true; }

/// <summary>
/// 机关函数应用False时：单个AND无效，多个AND无效；单个OR有效，多个OR有效；混应时写在OR后面的AND有效 
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> False<T>() { return f => false; }

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);
}

public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.And(expr1.Body, invokedExpr), expr1.Parameters);
}
}